Clamping means for grain cleaning apparatus



Nov. l, 1966 R. D. MITCHELL CLAMPING MEANS FOR GRAIN CLEANING APPARATUS5 Sheets-Sheet 1 Original Filed Nov. 22, 1961 Nov. 1, 1966 R. D.MITCHELL 3,282,423

` CLAMPING MEANS FOR GRAIN CLEANING APPARATUS Original Filed Nov. 22,1961 5 Sheets-Sheet 2 INVENToR.

ROBEIISQYT D. Mr-VCHELL @MQL/ww Nov. 1, 1966 R` D. MITCHELL.

CLAMPING MEANS FOR GRAIN CLEANING APPARATUS Original Filed Nov. 22, 19615 Sheets-Sheet 5 mmv mw mw] .mm/w@ INVENTOR. ROBEYRT D MWCHELL W4/5WATTORNEKSL.

Nov. 1, 1966 R. D. MITCHELL. 3,232,423

CLAMPING MEANS FOR GRAIN CLEANING APPARATUS Original Filed Nov. 22, 19615 Sheets-Sheet 4 INVENTOR. Roai; D. MWCHELL MAGL/band ATToe/vEY-s.

Nov. l, 1966 R. D. MITCHELL.

CLAMPING MEANS FOR GRAIN CLEANING APPARATUS 5 sheets-sheet 5 OriginalFiled Nov. 22, 1961 INVENTOR. ROBERT D. M TCH ELL ATTORNEYS.

United States Patent O 3,2s2,423 i CLAMPING MEANS FOR GRAIN CLEANINGAPPARATUS Robert D. Mitchell, Buffalo, N.Y., assigner to S. Howes Co.,Inc., Silver Creek, N.Y. Original application Nov. 22, 1961, Ser. No.154,245. Divided and this application Apr. 29, 1965, Ser. No.

2 Claims. (Cl. 209-319) This application is a division of my copendingapplication, Serial No. 154,245, filed November 22, 1961, now abandoned.

This invention relates to apparatus for cleaning dry granular materialby removing therefrom various undesirable material. For inst-ance, theapparatus may be usefully employed in cleaning lcereal grain byseparating therefrom dust, chaff, seeds, undersize grain, dirt, andother foreign matter.

The apparatus of the present invention, spe-aking :generally, employsseveral superposed vibratory classifying screens in conjunction with aircurrents for carrying off chaff and other light undesired particles andmaterial. The use of this general arrangement for cleaning grain is wellknown and the present invention is directed, among other things, to animproved general arrangement and cooperation of several of thefunctional components of grain cleaning apparatus of the gener-al typeindicated above.

While this application discloses and discusses the improvements of thepresent invention particularly with reference to cleaning apparatus forcereal grain, certain of the novel principles and teachings of theinvention are applicable to apparatus for grading and separating otherdry granular material according to different types and sizes and arealso applied to combined apparatus for both grading and cleaning thegrain or other dry granular material.

An object of the present invention is to provide a novel retention andlocking arrangement for the screen members and means are providedwhereby a single control may be manipulated to lock all of the severalscreen members of any number of principal screen surfaces of the screendeck in operating position or to release all of the screen memberssimultaneously by a single manipulation. The sc-reen retaining means isfurther so arranged that releasing movement thereof raises the screensections from their seats in the screen frames to further facilitatetheir removal from the apparatus.

Other objects and advantages of the grain cleaner apparatus of thepresent invention will become apparent to those skilled in this art froma study of the exemplary form hereinafter set forth. However, while aparticular embodiment is illustrated in the accompanying drawings and isdescribed in detail in the following specification, it is to beunderstood that such embodiment is by way of example only and that theprinciples of the invention may be variously applied and employed. Thespirit and scope of the invention is not to be considered as limited tothe form set forth herein by way of example nor otherwise than as denedin the appended claims.

4In the drawings:

FIG. 1 is a general side elevational view of one form of the graincleaner apparatus of the present invention;

FIG. 2 is an end elevational view of the `appar-atus of FIG. 1 viewedfrom the right hand end of FIG. 1;

FIG. 3 is a schematic view taken similarly t-o FIG. 1 showing the air owpassages and other portions of the apparatus diagrammatically;

FIG. 4 is a fragmentary top plan View of a portion of 3,282,423-Patented Nov. l, 1966 ICC the screen and screen housing structure of theapparatus of FIGS. 1 and 2, partly in cross-section; and

FIG. 5 is a fragmentary cross-sectional view taken generally asindicated by the line V-V of FIG. 1 but on a larger scale.

Like characters of reference denote like parts throughout the severalfigures of the drawings. In the exemplary embodiment of the inventionset forth herein to illustrate the various novel principles and featuresof the invention a rigid framework of horizontal and vertical structuralmembers designated. generally by the numeral 20 supports the Variousoperating components of the machine in their proper relative positions.

.In general the upper portion of the machine includes a feed box orentry arrangement for the grain to be cleaned and a blower or fan withappropriate duct work for Connecting the suction side thereof to take uprelatively light undesired matter from the grain being cleaned. Thisupper portion is shown schematically in FIG. 3. The lower portion of themachine is given over principally to a so-called screen deck whichcomprises a series of slightly inclined superposed. vibratory orreciprocatory screens with brush means for maintaining the screens clear.and effective to accomplish their screening functions. The screen deckstructure and the brushing mechanism are illustrated mainly in FIGS. 4and 5.

Mounted generally centrally of the upper portion of the machine is acentrifugal fan or blower designated generally by the numeral 21 andhaving its axis of rotation extending lengthwise of the machine, thatis, from the feed end to the delivery end. Blower 21 has two axial inletports designated 22 and 23 which are directed, respectively, toward thehead or feed end of the machine and toward the tail or delivery end.

Blower 21 discharges laterally, as at 24, air which in normal operationhas picked up and subsequently discharged chaff, light dirt and dust andother foreign matter which it draws from the grain and is separated fromin a manner which will presently appear. The rotor shaft of fan orblower 21 is shown at 25 in FIG. 2.

As will be noted from a consideration of FIGS. 1 and 3, blow-er inletport 22 communicates with a head chamber 26 and blower inlet port 23communicates with a t-ail chamber 27. Mounted .alongside of the headchamber 26 at the extreme right hand side of the machine as viewed inFIG. 1 is a feed. box 30 into which the grain to be cleaned isdeposited.

As schematically indicated in FIG. 3 the hoods which form the head andtail chambers 26 and 27 are separable from the underlying duct structuregenerally along a horizontal plane through the axis of blower rotorshaft 25. Thus removal of the head and tail chamber hoods exposes theair passage duct portions for ready access for cleaning or otherpurposes.

Referring to the schematic view, FIG, 3, a desired ilow4 of grain fromfeed box 30 passes into the lower portion of a vertical duct or suctionleg 31 which leads upwardly to the head chamber 26, the grain droppingto the head end of a screen deck or housing shown generally in FIGS. 1and 3.

The feed box 30 land the means for cont-rolling the rate of grain feedtherefrom are best shown in FIG. 3 wherein the numeral 32 designates anentry or ller duct and the numerals 33 and 34 designate a pair ofinclined wall members which converge downwardly to fonm a restrictedgrain passageway. y

A helical screw conveyor distributor member 35 is disposed in the apexformed by the wall members 33 and 34 and the helical formations thereofare of opposite hand in both directions outwardly from the center of thescrew member toward its ends. Accordingly, grain owingl downwardly tothe screw member 35 is distributed outwardly toward the opposite ends ofthe trough formed by the wall members 33 and 34 so that the grain ismore or less uniformly distributed along the feed box 30 which iselongated in a direction perpendicular to FIG. 3.

From the aforesaid trough the gain falls to a further pair -of inclinedtrough-forming walls members 37 and 38, the former of which is xedwithin the feed box 30 and the latter of which is attached to severalarms 39 which are fixed to an adjusting rockshaft 40 mounted in bearingsat the outside of feed box 30. A feed wheel 41 is mounted in the troughformed by the wall members 37 and 38 and is provided with vanes whichextend downwardly therealong in an axial direction whereby grain is feddownwardly -through the trough by rotation of feed wheel 41.

Means are provided for regulating the rate of feed of the grainindependently of the speed of rotation of the feed wheel 41 by movingthe adjacent portion of the wall member 38 toward and awayfrom feedwheel 41 to reduce or enlarge the passageway. It will be noted from FIG.3 that rockshaft 40 is provided with control arms 44 which terminate incam followers 45 which engage adjustable control cams 46. Extension coilsprin-gs 47 hold followers 45 in engagement with cams 46.

The springs 47 also provide a yieldable means for urging the movablewall member 38 toward the fixed wall member 37. Thus when unusuallylarge pieces of material must pass between these wall members the wallmember 38 may move resiliently away from wall member 37 to permit suchpassage, by rotation of feed wheel 41, without damage to the plates orassociated mechanism. After the large piece has passed between the wallmembers the spring 47 will return wall member 38 to its adjustedposition.

Cams 46 are xed to a camshaft 49 and a handwheel 50, shown in FIG. l,regulates the angula-r positions of cams 46 by way `of a worm and wheelconnection with camshaft 49 as at 51. The distributing screw member 35and the feed wheel 41 are belt connected as shown at 53 in FIG. 2 forrotation in the same direction at approximately the same speed, thescrew member 35 being driven from feed wheel 41 as will later appear.

As shown in FIG. 2, an electric driving motor 60 mounted on the top offramework 20 is belt connected as at 61 to the rotor shaft 25 `of blower21 to drive the same. A further belt connection 59 from shaft 25 extendsto a speed reducing gear unit 62 having an output shaft 63 and feedwheel 41 is belt connected to the latter as indicated at 64 in FIGS. land 2.

Reference will now be had to the screen deck structure, Va h-ousing forwhich is indicated generally by the reference numeral 65 in FIG. l andfurther details of which are shown more particularly in FIGS. 4 and 5.

Referring to FIG. l, the screen deck structure c-omprises generally ahousing having side walls 66 and top and bottom walls 67 and 68. Theside walls 66 extend generally longitudinally and in a downwardlyinclining direction toward the tail end o-f the machine, the left handend as Viewed in FIG. 1. At the right hand end the housing is enlargedupwardly as clearly shown at 69 in FIG. 1, thus forming a receivingchute for material falling from the feed box 30.

The screen housing is suspended for reciprocatory movement in agenerally left-to-right horizontal direction as viewed in FIG. 1 bypairs of f-ore and aft exible steel straps designated 70 and 71,respectively, which straps are attached to the machine framework attheir upper ends and to the screen housing structure at their lowerends. The screen housing structure is adapted to be rapidly reciprocatedfor effective vibratory screening action by a conventional eccentricdrive mechanism designated 73 in FIG. 1. A typical drive of this type,known in the art as a Buhler drive, is shown in Roth Patent No.1,517,587.

In the present instance the eccentric drive mechanism 72 is driven froma countershaft 75 by a belt connection 76 and the countershaft 75 isdriven from the output shaft 63 of speed reducer 62 by a belt connection77.

Supporte-d between the side walls 66 of the screen housing structure area series of three superposed screens including a relatively shortscalper screen 80, shown in dot and dash lines in FIG. 3, which ispositioned in the upwardly extending right hand portion 69 of the screenhousing and inclines downwardly to the right as viewed in FIGS. 1 and 3.The remaining two screens, one above the other, are designated 81 and 82and incline downwardly to the left as viewed in FIG. l. The upper screen81 is generally called the main screen and the lower screen 82 is calledthe sand or seed screen. Each of these screens in the present instancecomprises two screen units in edge -to edge relation, as will laterappear.

The scalper screen 80 receives the grain falling from the feed box 30 byway of the suction leg 31 and since the scalper screen is -of relativelycoarse mesh it passes all excepting the larger pieces of foreign matter-or debris, the latter being discharged from 4the machine by way of achute designated in FIG. 1.

The main screen 81 is of such mesh as to pass good grain but holdthereon all undesired matter larger than the good grain. The lowermostscreen 82 which finally receives the grain through Ithe main screen isof relatively fine mesh and merely passes sand, seeds and similar fineimpurities which are generally of smaller particle size than the goodclean grain. Foreign matter held on main screen 81 discharges through achute 83 and nes falling through screen 82 to bottom pan or wall 68 passout 0f the machine through a duct 84.

The screen deck structure is fthe subject of further novelty as to themeans and method of mounting and releasably securing the screen elementstherein and as to the means provided forbrushing the bottoms of thescreens to maintain the same clear and unclogged for performing theirscreening functions. Further details of the screen structure will bedescribed later herein, following a description and discusison of thegeneral structure and operation of the grain cleaner generally. In thisconnection reference will now be had to the diagrammatic View, FIG. 3,which presents the grain cleaner as viewed in FIG. 1 but in schematicform.

The feed box 30 and its adjunots and the suction leg 31 adjacent theretohave been previously described, as

has the blower 21 and its two inlet ports 22 and 23 and its dischargeduct 24. It will be noted from FIG. 3 that good grain from the lower endof the nal screen 82 discharges into the lower end of a vertical duct 85called herein the tail air suction leg. It will be noted also that thehead and tail suction legs 31 and 85 discharge at their upper ends intothe head and tai-l chambers 26 and 27, respectively.

To promote precipitation of chaff and other light materials from the airpassing from the suction legs 31 and S5 through the head and tailchambers 26 and 27 and to the blower 21 the head and tail chambers areeach provided with a series of bales which cause the air to pursue aItortuous expanding path through the head and tail chambers. Thisexpansion of the area of the flow path in the direction of ow reducesthe velocity of the air whereby solid particles entrained therein fallinto hoppers 86 and 87 at the lower ends of these chambers, from whenceit is moved laterally from the machine by means of a pair of conveyorscrews 88 and 89, respectively.

Referring to the head chamber 26, a pivoted damper plate 90 regulatesthe passage area between the suction leg 31 `and chamber 26. A similarlylocated pivoted damper plate 91 is provided in the tail chamber 27 toregulate the flow area between tail suction leg 85 and chamber 27 andmanual adjusting control means for the damper plates 90 and 91 areprovided externally of the machine as shown at 92 and 93, respectively,in FIG. l.

Air passing into the blower inlets 22 and 23 from the head and tai-lchambers goes by way of fan or blower inlet chambers designated 95 and96, respectively, which communicate at their upper ends with the head4and tail chambers, such communication being under the control of slidedampers 98 and 99, respectively, which are regulated vertically by screwmechanism designated 100 and 101, respectively.

It is desiredthat air entering the headand tail chambers flowdownwardly, thence upwardly to the blower inlet chambers, to furtherpromote precipitation of solid matter entrained in the air. Accordinglythe head and tail chambers are provided with fixed bales designated 102and 103, respectively, which extend downwardly from the upper ends ofthese chambers medially between their entry and discharge sides.

It will be noted that air passes upwardly through the scalper screen 80to suction leg 31 to entrain chaff, dust and other light impurities fromthe grain as it enters the screen structure. Again at the discharge end,the screened grain falls into the tail suction leg wherein air ispassing upwardly to the blower to entrain chaff and other relativelylight material which has not been previously separated or which wasremoved from the grain in the course of the cleaning and screeningprocess.

As shown in FIG. 1, the chaff hopper screw conveyors 88 and 89 areconnected for joint rotation by a belt 104, the conveyor screw S8 beingdriven from the output shaft 63 of speed reducer 62 by a belt connection105.

The effective suction at the head and tail ends of themachine may beindependently regulated by means of a pair of sliding valve plates 107and 108 located against upper wall portions of the blower inlet chambers95 and 96, respectively. The valve plates 107 and 108 and the underlyingwall portions of the inlet chambers each have Va multiplicity ofperforations, as indicated in FIG. 3, and the inlet chambers may thus beselectively vented to atmosphere in varying degrees by reason of thefact that the perforations of the valve plates are in registry with theunderlying perforations in the inlet chamber walls in greater or lessdegree, according to the horizontal positions of adjustment of the valveplates. The valve plates 107 and 108 may be entirely closed by movingthe plates so that the respective perforations of the plates and thewall portions are entirely out of registry.

Flow of good grain from screen 82 into tail leg 85 by way of a chute 110may be controlled or arrested as desired by vertical adjustment of asliding valve plate 109 associated with the ta'il leg 85.

Reference will now be had to further details of the construction andoperation of the screen deck structure illustrated particularly in FIGS.4 and 5. As indicated earlier herein, both the main screen 81 and thelowermost screen 82 comprise two screen sections lying in abuttingrelation, each section extending the full width of the screen deck. Themanner in which these screen sections are supported and retained in thescreen deck housing is shown in detail in FIG. 5, wherein the numeral120 designates an angle iron rail member fixed to the interior wall of aside wall 66 of the screen housing 65. It is to be understood that twopairs of rail members 120 are provided, an upper and a lower rail memberat the inter-ior of each side wall 66 to provide ledges for supportingthe opposite side edges of the screens 81 and 82.

The screen member 82 which is illustrated fragmentarily in FIG. `5includes a frameV portion 121 of channel cross section which extendsthereabout and is adapted to rest on the rail members 120 at oppositesides of the screen housing. In the illustrated instance frame portion121 is tapered as shown to it between wedge shaped longitudinal gasketmembers 122 `of rubber or the like whereby the screen members fit snuglybetween the houssing side walls 66. For conveniently and securelylocking the screen members 81 4and 82 in assembled position and forreleasing them when desired the following locking arrangement isprovided.

A longitudinal locking or clamping Ibar overlies each rail member 120and is provided with inwardly projecting yoke portions 126 at itsopposite ends which are pivoted to the upper ends of the rock arms, therock arms at the feed end being designated 127 in FIG. y1 and the rockarms at the delivery end being designated 128 in FIGS. 1 and 5. The rockarms 127 at the feed end of the screen housing are fixed to the innerends of rock shafts 130 which are jointly oscillated to effect lockingmovements of the screen members 81 and 82 in `a manner which will now bedescribed.

Exteriorly of the sidewalls 66 of the screen housing the rock shafts 130are connected for joint rocking movement by arms 131 and a connectinglink 132. As shown in FIG. l, an operating screw 135 is mounted at thefeed end of screen housing 65 as at 136 for free rotation but in amanner to prevent -axial movement. An operating handle 137 is providedat the outer end of screw 135 and its inner end engages an internallythreaded arm (not shown) on a rock shaft 138. Rock shaft 138 hasoperating connection with the rock shafts 130 at opposite sides of thescreen housing 65 by means of rock arms 140 and 141 and a connectinglink 142.

From the fore-going it will be seen that operation of screw 135 in onedirection or the other by manipulation of handle 137 will rock theseveral arms 127 in opposite directions. Since each arm 127, itscompanion arm 128, and the connecting locking or clamping bar 125 form,in conjunction with the side wall 66 to which the arms 127 and 128 arepivoted, a parallelogram linkage, rocking movements of the 4arms 127 areautomatically duplicated in the several arms 128. v

. Thus all of the locking yor clamping bars 125 are jointly raised andlowered in a parallel manner by manipulation of handle member 137 ofscrew 135. This operation either clamps the lower flanges of the severalscreen framing channels 122 to the supporting rail members 120 orreleases them. Raising movements of the locking bars 125 causes them toengage the upper interior portions -of the screen framing channels 121to raise the screen sections clear of the supporting rail members 120for ready removal.

In grain cleaners of the prior art it is customary to provide means forcontinuously brushing the under surfaces of the screens to maintaintheir effectiveness. The apparatus of the present invention providesnovel means for -accomplishing this function in the form of fluidpressure actuated motor means which acts directly upon the brushsupporting structure to reciprocate the same without mechanicalconnection to or transmission from the screen housing structuregenerally.

This is of particular advantage because of the vibratory action of thescreen structure and the desirability of isolating the same from theremainder of the machine as far as is practically feasible. In the`arrangement of the apparatus of the present invention the supportingand driving means for the brush mechanism is mounted independently ofthe screen structure itself.

Refe-rring particularly to FIGS. 4 and 5, a general-ly rectangular brushsupporting frame is -designated by the numeral and a plurality oflongitudinal rows of lbrush members is designated 151. The lateralspacing of the r-ows of brush members is -approximately equal to orslightly less than the degree of lateral reciprocation of the brushsupporting frame 150 so that the entire under surface of the screens iskept clear and it will be noted that the individual brush members ofeach row are spaced from each other a short distance whereby they cleara series of lateral reinforcing angle members 152 0f the screen members81 land 82.

The supporting and reciprocating means for the brush supporting fname150 is illustrated in FIG. 4, to which reference will now be had. Asindicated above, the

brush frame support is independent of the remainder of the screenstructure, including the screen housing. A pair of tubular brush framesupport shafts 155 and 156 extend laterally through the screen housingjust below each of the screen members 81 and 82 and the two pairs ofshafts 155 :and 156 are xed at their opposite ends to the generalframework of the apparatus as indicated in FIG. 4.

Fixed to the underside of each brush frame 150 adjacent to its fourcorners are bearings 160, preferably of the lineal ball type, whichmount the brush f-r-ame on the tubular shafts 155 and 156 for lateralsliding movement. Reciprocation of each brush frame 150 is effected byan air cylinder 161 which is attached at one end to the machineframework 20 las at 162 and has a piston rod 164 which is attached atits outer end to the brush frame 150 as at 165. It will be seen from theforegoing that both the reciprocable mounting of each b-rush frame andits reciprocating means are supported entirely independently of thescreen housing generally.

Each cylinder 161 is double acting and is provide-d with conventionalconduit and passage means for supplying operating air pressurealternately to its opposite ends. The means for shifting the valvepositions at each end of the lateral movement of the brush frame willnow be described. A valve shifting rod 168 extends through the tubularbrush frame mounting shaft 156 and engages a shifting lever 169 of avalve shifting mechanism 170.

A pair of valve shifting collars 171 and 172 are slidably mounted -onshaft 156 at each side of the screen housing just inwardly -of the sidewalls 66 thereof and studs 174 extend through the collars 171 and 172and into valve shifting rod 168 whereby the collars 171 and 172 and thevalve shifting rod 168 are fixed for joint axial movement. The studspass through longitudinal slots in shaft 156 to permit such movementindependently of shaft 156.

As a brush frame 150 reaches its limit of movement in either directionone of the bearings 160 thereof which slides on shaft 156 during suchmovement abuts an adjacent valve shifting collar 171 or 172, as the casemay be, and thus moves valve shifting rod 168 to reverse the valveshifting mechanism 170 and thus reverse the direction of piston rod 164and brush frame 150.

In FIG. 1 the numeral 180 designates an air pressure storage tank whichmay be employed to supply operating fluid pressure to the brushactuating cylinders 161, pressure thereafter being generated by an aircompressor 181 driven from shaft 75 by a belt connection 182. Ifdesired, side panel members may be attached to the exterior of framework20 to enclose the working parts of the apparatus.

In FIGS. 4 and 5 the numerall 185 `designates a series of angle memberswhich are secured to the upper surfaces of the frame portions 121 of thescreen members in obliquely disposed position, as shown in FIG. 4. Graintending to move downwardly along the screen frame portion is thus4deflected inwardly. to the screen surface proper at various pointsalong the side edges of the screen surfaces.

Iclaim:

1. In a grain cleaner, a screen housing comprising opposed side wallsand opposed vertically spaced pairs of rails at the interiors of saidside walls, a screen section adapted to seat on each pair of said rails,an opposed pair 0f llocking bar members disposed above each pair of saidrails, longitudinally spaced rock yarms on each of said bar membersmounting the latter for parallel movement toward and away from saidrails linkage means connecting between a pair of vertically spaced rockarms at a corresponding longitudinally spaced position on at least oneside of said screen housing forming with said bar members aparallelogram 'linkage 'at said one side, and common control meansoperable to simultaneously move each opposed pair of said locking barmembers toward and away from said rails to selectively clamp and releasesaid screen sections.

2. In a grain cleaner, a screen housing comprising opposed side wallsand opposed pairs of rails at the interiors of said side walls, aplurality of screen sections adapted to seat marginally on said rails, aplurality of vertically spaced locking bar members disposed 4above saidrails, longitudinally spaced rock arms mounting said bar members forparallel movement toward Iand away from said rails, and control meansincluding linkage means connecting rock arms of the several locking barmembers forming with said several locking bar members a parallelogramlinkage and operable to simultaneously move said plurality of lockingbar members toward and away from said rails to selectively clamp andrelease said screen sections.

References Cited by the Examiner UNITED STATES PATENTS 1,919,485 7/ 1933Soldan 209-403 2,227,090 12/ 1940 Hughes 209-404 X 2,426,897 9/ 1947Orton 209-405 X 2,477, 123 7/ 1949 `Gilson 209-319 3,022,893 2/1962Hasley 209-319 X 3,087,617 4/1963 Forsberg 209-319 FOREIGN PATENTS509,591 7/ 1939 Great Britain.

HARRY B. THORNTON, Primary Examiner.

1. IN A GRAIN CLEANER, A SCREEN HOUSING COMPRISING OPPOSED SIDE WALLSAND OPPOSED VERTICALLY SPACED PAIRS OF RAILS AT THE INTERIORS OF SAIDSIDE WALLS, A SCREEN SECTION ADAPTED TO SEAT ON EACH PAIR OF SAID RAILS,AN OPPOSED PAIR OF LOCKING BAR MEMBERS DISPOSED ABOVE EACH PAIR OF SAIDRAILS, LONGITUDINALLY SPACED ROCK ARMS ON EACH OF SAID BAR MEMBERSMOUNTING THE LATTER FOR PARALLEL MOVE MENT TOWARD AND AWAY FROM SAIDRAILS LINKAGE MEANS CONNECTING BETWEEN A PAIR OF VERTICALLY SPACED ROCKARMS AT A CORRESPONSING LONGITUDINALLY SPACED POSITION ON AT LEAST ONESIDE OF SAID SCREEN HOUSING FORMING WITH SAID BAR MEMBERS APARALLELOGRAM LINKAGE AT SAID ONE SIDE, AND COMMON CONTROL MEANSOPERABLE TO SIMULTANEOUSLY MOVE EACH OPPOSED PAIR OF SAID LOCKING BARMEMBERS TOWARD AND AWAY FROM SAID RAILS TO SELECTIVELY CLAMP AND RELEASESAID SCREEN SECTIONS.